Surface decorative plates used for furniture or cabinets of kitchen wares generally have such a laminated structure in which a decorative sheet having, for example, a printed woodgrain pattern thereon is bonded onto a wood material, an inorganic material, a synthetic resin-based material, a metallic material such as steel plate, etc., through an adhesive.
The decorative sheet used for the surface decorative plates has been required to exhibit various properties, e.g., adequate processing suitability such as flexibility, cuttability and breaking resistance for secondary processing such as laminating, wrapping and V-cutting, as well as weather resistance, light resistance, heat resistance, water resistance, solvent resistance, surface hardness, abrasion resistance, marring resistance, etc., upon use.
To meet these requirements for the decorative sheet, there has been used a substrate fully satisfying the above processing suitability which is provided on a surface thereof with a surface protective layer. The suitable surface protective layer conventionally used has been made of an ionizing radiation-curable resin composition. The ionizing radiation-curable resin composition is cured when exposed to an ionizing radiation such as ultraviolet ray and electron beam. The use of such an ionizing radiation-curable resin composition have various advantages such as solvent-free and environment-favorable formation of the surface protective coating layer without using an organic solvent, easy achievement of a good surface strength such as abrasion resistance owing to a high crosslinking density thereof, etc.
Meanwhile, with the recent tendency of consumers toward high-grade products, floor tiles and wall panels as well as furniture and cabinets of kitchen wares have been required to show a high-grade feeling. The decorative plates and decorative sheets used in these products have also been demanded to exhibit a good appearance with a high-grade feeling. For this reason, it becomes important to impart a good texture to these products by printing various patterns on a surface of a substrate sheet, or laminating a film with a pattern layer thereon, and there have been proposed various methods such as the method of delustering specific portions of the patterns or forming convex and concave patterns on such portions to impart a good texture thereto.
For example, there has been proposed the method in which surface regions which are different in wettability to an electron beam-curable coating material or a photocurable coating material from each other are formed on a substrate by providing a patterned coating layer on the substrate, and then the electron beam-curable coating material or the photocurable coating material is applied onto the substrate to recess a surface of the applied coating material in the surface region having a good wettability to the coating material and raise a surface of the applied coating material in the surface region having a poor wettability to the coating material (for example, refer to claims of Japanese Patent Publication No. 26937/1976). However, the above method has such a problem that when the concave portions, i.e., the surface region having a good wettability to the coating material is narrow, neat convexo-concave patterns are unattainable thereon. Further, although the existence of concave portions which are thick to some extent allows formation of convexo-concave patterns on the surface of the substrate, an end portion at which transition from the convex portion to the concave portion or vice versa occurs, is rounded at a boundary region between the recessed and raised portions due to a surface tension of the coating material, etc. As a result, there tend to arise problems such as lacking of sharpness of the convexo-concave patterns and formation of convex portions having a larger height than that of the raised portions, which results in lacking of reality, for example, in the case of woodgrain patterns, and poor appearance and touch feeling.
There has also been proposed the method in which a film on which a multicolor pattern is printed with an ink containing a curing retarder for retarding curing of resins in a solvent-free coating material and an ink containing no curing retarder is laminated on a resin coating layer formed by previously applying the solvent-free coating material on a substrate, the resin is cured in a curing atmosphere, and then the film is peeled off from the substrate to transfer the multicolor pattern onto the substrate (refer to claims of Japanese Patent Publication No. 33454/1976). According to this method, only the color pattern portion printed with the ink containing a curing retarder can be transferred and recessed. However, the above method not only requires use of the special inks, but also has such a problem that a curing reaction of the resin coating layer produced from the solvent-free coating material is unstable.
Further, there has been proposed the decorative material composed of two kinds of pattern layers successively formed on a substrate, i.e., a pattern layer made of an ordinary ink and a convex pattern layer made of an electron beam-curable composition, and a transparent resin layer formed on the pattern layers, in which after coating, the convex pattern layer is cured by irradiating an electron beam thereto through the transparent resin layer (refer to claims of Japanese Patent Publication No. 41505/1989). However, the decorative material has physically large convexo-concave portions and therefore tends to suffer from flaws or scratches in the convex portions. This tendency is more remarkable in the case where the convex portions have a larger surface area. Also, in this method, when it is intended to obtain a contrast of gloss such as, for example, woodgrain patterns, namely form a pattern having convex portions as a large part and very narrow concave portions between the convex portions like vessel grooves of woodgrain, there tends to arise such a problem that the concave portions are buried due to flowing of the coating material for forming the transparent resin layer, and the extent of burying of the concave portions becomes inadequately uneven, and further such physical convexo-concave portions cause a poor touch feeling.
In addition, there has been proposed the decorative paper with a woodgrain pattern which is produced by solid-printing a wooden undercoating color on a thin paper with an ultraviolet-curable printing ink containing a delustering agent, irradiating an activation light ray to the resultant undercoat, printing a woodgrain pattern on the undercoat with a high-gloss ultraviolet-curable printing ink, and then irradiating an activation light ray to the thus printed woodgrain pattern (refer to claims of Japanese Patent Application Laid-Open No. 84910/1976). In the decorative paper, portions printed with the high-gloss ink appear like convex portions, whereas portions printed with the ink containing the delustering agent appear like concave portions, thereby imparting a woody texture to the decorative paper. However, since the thus proposed decorative paper is provided with no transparent topcoat as a protective coating film, portions corresponding to the so-called vessel-printing ink used for printing a woodgrain pattern are deteriorated in weather resistance, water resistance, abrasion resistance, marring resistance, etc., namely, shows a poor durability.
Further, there has been proposed the method for producing convexo-concave patterns by forming a pattern made of an ionizing radiation-shielding material on either a front or back surface of an ionizing radiation-penetrating release substrate having a surface releasability, laminating a convexo-concave pattern-forming substrate having a layer made of an uncured ionizing radiation-curable resin on a surface thereof on the release substrate, irradiating an ionizing radiation to the resultant laminate from a side of the release substrate to cure only the ionizing radiation-curable resin located corresponding to non-patterned portions made of the ionizing radiation-shielding material, and then removing the uncured resin in the ionizing radiation-curable resin layer together with the release substrate (refer to claim 8 of Japanese Patent Application Laid-open No. 253449/1989). According to the method of this invention, in the patterned portions made of the ionizing radiation-shielding material, the ionizing radiation-curable resin is kept uncured and attached to the release substrate, and removed together with the release substrate, whereas in the non-patterned portions made of the ionizing radiation-shielding material, the ionizing radiation-curable resin remains in a cured state on the substrate so that the convexo-concave patterns coordinated with aimed patterns are formed on the substrate. However, this method has disadvantages such as need of special materials such as the release material and the ionizing radiation-shielding material. Further, in the above method, since the uncured resin is attached to the release substrate and removed together therewith, there tend to occur problems such as failure of forming deep and sharp concave portions. In addition, in the case where an electron beam-curable resin is used as the ionizing radiation-curable resin, it is difficult to select a suitable electron-beam-shielding material.
Also, there has been proposed the method for producing a decorative plate with convexo-concave patterns by applying a radiation-polymerizable synthetic resin onto a printed or decorative paper-laminated substrate, irradiating a radiation onto the obtained synthetic resin layer until the synthetic resin reaches a semi-cured state, pressing the semi-cured layer using a cold pressing member such as a roll press with corresponding convexo-concave patterns, and then completely curing the synthetic resin (for example, refer to claims of Japanese Patent Publication No. 28264/1974). However, it is difficult to determine the specific conditions for keeping the resin in a suitable and stable semi-cured state, and the semi-cured synthetic resin is unstable. Further, this method has problems such as need of the complicated two-stage curing procedure.
In consequence, there has also been proposed the method for continuously forming convexo-concave patterns by applying an electron beam-curable resin on a substrate using a coating apparatus, and irradiating an electron beam to the applied electron-beam-curable resin while contacting the resin with a molding roll with corresponding convexo-concave patterns within an electron-beam irradiating apparatus to impart the convexo-concave patterns of the molding roll to the cured resin (for example, refer to claims and FIG. 1 of Japanese Patent Publication No. 50066/1988). However, this method has such an inconvenience that not an ordinary printing apparatus but the special molding roll apparatus is required to form the convexo-concave patterns, and the molding roll has only a limited pattern-forming speed, resulting in poor yield.
Further, there has been proposed the decorative material which is successively provided on a surface of a substrate with a coating film layer, a pattern layer and a surface protective layer made of a crosslinked and cured ionizing radiation-curable resin composition in which the pattern layer exhibits a higher penetrability to the ionizing radiation-curable resin composition than that of the coating film layer (for example, refer to claims and FIGS. 1 and 2 of Japanese Patent Application Laid-open No. 199028/2001). In the decorative material, since the ionizing radiation-curable resin composition tends to be readily penetrated into portions where the patterns are present, the portions to which the ionizing radiation-curable resin composition is penetrated are formed into concave portions, thereby obtaining a decorative material having convexo-concave patterns on a surface thereof. However, in the decorative material, it is required to add a large amount of an extender pigment or a porous material to the pattern layer in order to impart a sufficient absorptivity and penetrability to the pattern layer. In this case, since the pattern layer has a porous structure and therefore tends to become brittle, the resultant convex portions of the decorative material tend to be deteriorated in durability and stain resistance. On the other hand, when it is intended to inhibit the pattern layer from being formed into a porous structure in order to enhance a durability and a stain resistance of the convex portions, there arises such a problem that the convex portions are insufficient in depth and sharpness. Further, the decorative material have physical convexo-concave portions and therefore exhibit a poor touch feeling which must be further improved.
Further, in the case where the decorative material is used in shelves of a kitchen cabinet, etc., even though its surface protective layer is made of a crosslinked and cured product of the ionizing radiation-curable resin, edible oils attached onto the surface of the decorative material tend to penetrate to an inside thereof, resulting in increase in transparency at the oil-penetrated portions and, therefore, causing the portions to remain with a water-wetted appearance, i.e., a so-called wet color.
As a matter of course, if the thickness of the surface protective layer is increased to several tens μm, the surface protective layer forms a dense layer, thereby preventing the oils from penetrating underneath the surface protective layer and inhibiting the wet color from occurring thereon. However, when the surface protective layer having a large thickness is made of the ionizing radiation-curable resin which tends to form a harder layer than thermosetting resins, the resultant decorative material tends to be deteriorated in flexibility and become difficult to store in the form of a roll, and further the costs of materials therefor tend to be increased. Therefore, in view of the storage and costs, the thickness of the surface protective layer is usually 10 μm or less and preferably as small as possible, as long as the layer can maintain a suitable performance. On the other hand, as the thickness of the surface protective layer is reduced, influence of a coating solution penetrating into the substrate tends to become more considerable upon forming the surface protective layer. As a result, a denseness of the surface protective layer is lowered and voids formed therein are increased, so that oils attached onto the surface of the decorative material tend to more readily penetrate thereinto, thereby exhibiting a wet color.
In the case where the substrate itself is previously impregnated with a resin, even though the surface protective layer itself is slightly deteriorated in oil resistance to allow oils attached onto the surface of the decorative material to penetrate into the surface protective layer, the oils are inhibited from further penetrating into the resin-impregnated substrate. However, the problem that the surface protective layer itself has a poor oil resistance still remain unsolved. In addition to the above problem, a costly expensive resin-impregnated product is required as the substrate, and such a substrate tends to be deteriorated in flexibility.
In addition to the oil resistance, a marring resistance is also an important factor for the decorative material. The marring resistance is an anti-scratch property required for the decorative material separately from the oil resistance even when the decorative material exhibits a sufficient surface strength, for example, a high abrasion resistance by forming the surface protective layer from a crosslinked cured product of the ionizing radiation-curable resin. For the purpose of attaining a good abrasion resistance, the surface protective layer is usually hardened by adding a filler such as silica particles thereto. However, in particular, when adjusting a surface gloss of the decorative material by the surface protective layer for design expression thereof, the surface gloss tends to be undesirably increased owing to gathering of very fine scratches formed thereon. For example, when a number of decorative plates stuck together undergo swing or vibration motions and are rubbed with each other upon transportation thereof, or when handling the decorative plates in a production line thereof, the increase in surface gloss due to the gathered scratches tend to occur. Although such a condition that fine scratches are uniformly distributed over a surface of the decorative plate will be still suitable, when a part of the surface of the decorative plate undergoes repeated rubbing motions, spot-like difference in gloss on the surface tends to become remarkable, resulting in production of defective products. For this reason, the decorative material is required to have good a marring resistance capable of preventing occurrence of change in gloss even when the surface thereof is exposed to the rubbing motions.